Repulpable PSAs

ABSTRACT

The invention relates to a repulpable pressure-sensitive adhesive. Provision is made for the repulpable pressure-sensitive adhesive to comprise at least one polyacrylate-based block copolymer.

[0001] The invention relates to repulpable pressure-sensitive adhesives(PSAs) and also to PSA tapes, labels or other PSA articles equipped withthese PSAs and/or formulations thereof. The PSAs described are used withpreference in the paper-processing industry as repulpable and recyclableproducts.

BACKGROUND OF THE INVENTION

[0002] In paper processing and for the printing processes it isnecessary to splice papers in order to ensure a continuous operation.The splicing operation, and hence the PSA splicing tapes, are subject tovery stringent requirements, since even today operating speeds of morethan 1 500 m/min are entirely common. PSA splicing tapes must have agood tack, but should also have a high dimensional stability, forexposure to shearing. As well as the adhesive-related requirements, thePSAs ought likewise to withstand the operation of recycling the paper;that is, after reprocessing, there should be no tackiness from thesplicing tape remaining on the paper.

[0003] Moreover, in recent years, the reprocessing conditions for thepaper recycling operation have changed. Formerly, reprocessing wascarried out under acid conditions. At the present time the trend istowards reprocessing in a basic medium

[0004] With the aim of attaining the requirements referred to above, thepatent literature has already described a large number of different PSAtapes. The first repulpable splicing tape was described in U.S. Pat. No.2,838,421. There, polyacrylic acid was mixed with polypropylene glycolto produce a water-soluble PSA. U.S. Pat. No. 3,441,430 describes arepulpable PSA tape based on acrylic acid/ethyl acrylate copolymers andwater-soluble plasticizers having at least one ether function.

[0005] U.S. Pat. No. 3,661,874 discloses epoxidized rubbers which havebeen reacted with secondary monoamines and compounded with water-solubleplasticizers. DE 2 360 441 describes copolymers of acrylates andvinylcarboxylic acids which have in part been neutralized with liquidpolyoxyethylenes and/or with a reaction product of acidic resins andalkanolamines. The cohesion of these PSAs can be enhanced by usingethoxylated diamines as plasticizers (DE 3 105 894).

[0006] The splice strength at relatively high temperatures can beenhanced by using acrylamide (DE 3 901 690 and EP 0,081,846).Terpolymers of N-vinyllactams or N-vinylamides, acrylic acid and alkylvinyl ethers, disclosed in DE-C 34 23 446, likewise produce anenhancement of splice strength at high temperatures. Acrylic acid canalso be substituted by acryloyloxypropanoic acid (EP 0,352,442).

[0007] PCT/US 92/06731 discloses terpolymers composed of polar monomers,such as acids or hydroxyalkyl esters, for example, and less polarmonomers, such as acrylate-based alkyl esters, for example, and ofpolymerizable, water-soluble macromonomers. These terpolymers havelikewise been blended with water-soluble plasticizers and exhibited highrepulpability within a wide pH range.

[0008] The polymers cited above, however, possess the disadvantageeither that they cause problems in the alkaline reprocessing operation,by forming agglomerates, or that on papers containing calcium carbonatethey likewise form agglomerates, which significantly lower the tack ofthe polymer during adhesive bonding for a prolonged period.

[0009] There is therefore a need for a pressure-sensitive adhesive whichdoes not have the aforementioned disadvantages of the prior art.

SUMMARY OF THE INVENTION

[0010] The invention accordingly provides a pressure-sensitive adhesivewhich has a high splice strength and tack over a long period and inbasic media.

[0011] The repulpable pressure-sensitive adhesive of the inventioncomprises at least one polyacrylate-based block copolymer. The inventionfurther provides a repulpable pressure-sensitive adhesive tape which iscomposed of a backing material coated on at least one side with apressure-sensitive adhesive comprising polyacrylate-based blockcopolymers.

[0012] The block copolymers used in accordance with the invention arecharacterized by a sequence of “hard and polar” polymer blocks [P(A) orP(A/C)] having a high softening/glass transition temperature and of“soft and less polar” polymer blocks [P(B) or P(B/D)] having a lowsoftening/glass transition temperature, the block copolymersadvantageously comprising at least one triblock copolymer structure[P(A)-P(B)-P(A) and/or P(B)-P(A)-P(B), in which in each case P(A) can besubstituted by P(A/C) and/or P(B) by P(B/D)]. P(A/C) and P(B/D) denotepolymer blocks constructed as a copolymer of A and C and of B and D,respectively.

[0013] Some advantageous embodiments which can be used with particularadvantage in accordance with the invention are set out by way of examplebelow.

DETAILED DESCRIPTION

[0014] As PSAs useful in accordance with the invention it is possible,for example, to make outstanding use of those PSAs based on blockcopolymers of the general type P(A)-P(B/D)-P(A), in which each blockcopolymer is composed of a middle copolymer block P(B/D) and two endpolymer blocks P(A) where

[0015] P(B/D) represents a copolymer of the monomers B and D, withP(B/D) possessing a softening/glass transition temperature of from 0° C.to −80° C., component D possessing at least one functional group whichis inert in a free-radical polymerization reaction and which serves toincrease the cohesion of the block copolymer,

[0016] P(A) represents a polymer of the monomers A, with P(A) possessinga softening/glass transition temperature of from 20° C. to 175° C. andbearing at least one polar unit, such as a carboxylic acid, hydroxyl,amide, sulphonic acid or phosphoric acid group, for example,

[0017] the polymer block P(A) is insoluble in the copolymer block P(B/D)and the blocks P(A) and P(B/D) are immiscible.

[0018] By softening temperature is meant here a glass transitiontemperature for amorphous systems and a melting temperature in the caseof semi-crystalline polymers. The temperatures indicated here correspondto those obtained from quasi-steady-state experiments, such as DSC, forexample.

[0019] The cohesion-increasing effect of the copolymer P(B/D) can bebrought about advantageously by means of bonds between the individualblock copolymers P(A)-P(B/D)-P(A), the functional group of component Dof one block copolymer macromolecule interacting with at least one otherblock copolymer macromolecule. In a particularly advantageous way thefunctional group of component D brings about the increase in cohesion bymeans of dipole-dipole interactions and/or hydrogen bonds. Withparticular preference the functional group of component D is acarboxylic acid group, a hydroxyl group or a tert-butyl group.

[0020] As component B it is preferred to use at least one compound ofthe following general formula

[0021] where R₁=H or CH₃ and R₂ is selected from the group of branchedand unbranched, saturated alkyl groups having 4-14 carbon atoms.

[0022] As component A the monomers are preferably selected such that theresulting polymer blocks P(A) are capable of forming a 2-phase domainstructure with the copolymer blocks P(B/D). The fraction of the polymerblocks P(A) is very preferably between 10 and 60% by weight, inparticular between 25 and 50% by weight of the overall block copolymer.Additionally, the weight fraction of component D in relation tocomponent B is advantageously between 0 and 30% by weight, in particularbetween 0.5 and 20% by weight.

[0023] Another pressure-sensitive adhesive which can be usedoutstandingly in the inventive sense is based on block copolymers of thegeneral type P(B)-P(A)-P(B) or of the type P(B/D)-P(A)-P(B/D), eachblock copolymer being composed of a middle (co)polymer block P(A) andtwo end (co)polymer blocks P(B) or P(B/D) respectively, where

[0024] P(B) represents a (co)polymer composed of at least one monomer B,with P(B) possessing a softening/glass transition temperature of 0° C.or lower, or P(B/D) represents a copolymer of the monomers B and D, withP(B/D) possessing a softening/glass transition temperature of 0° C. orlower, component D possessing at least one functional group which isinert in a free-radical polymerization reaction and which serves toincrease the cohesion of the block copolymer,

[0025] P(A) represents a (co)polymer of at least one monomer A, withP(A) having a softening/glass transition temperature of 20° C. or higherand bearing at least one polar unit, such as a carboxylic acid,hydroxyl, amide, sulphonic acid or phosphoric acid group, for example,

[0026] the (co)polymer block P(A) is insoluble in the (co)polymer blockP(B) or P(B/D), and the blocks P(B) and also P(B/D) and P(A) areimmiscible.

[0027] Component D preferably includes at least one functional groupwhich is inert in a free-radical polymerization reaction and which mayserve to increase the cohesion of the block copolymer; in particular bymeans of bonds between the individual block copolymers, with thefunctional group of component D of one block copolymer macromoleculeinteracting with at least one other block copolymer macromolecule; inparticular by means of a crosslinking reaction. The functional group forincreasing the cohesion can with great advantage be a hydroxyl, acarboxyl, an epoxy, an acid amide, an isocyanato or an amino group, agroup comprising a photoinitiator for UV crosslinking, or an unsaturatedgroup.

[0028] With further advantage the block P(B) or P(B/D) possesses asoftening/glass transition temperature of between −80° C. and 0° C.and/or the block P(A) possesses a softening/glass transition temperatureof between 20° C. and 180° C.

[0029] The fraction of the (co)polymer blocks P(A) is preferably between30 and 70% by weight, in particular between 40 and 65% by weight of theoverall block copolymer. The weight fraction of component D in relationto component B is advantageously between 0 and 30% by weight, inparticular between 0.5 and 20% by weight.

[0030] Another pressure-sensitive adhesive which can be used withadvantage in accordance with the invention is one based on blockcopolymers of the general type P(A/C)-P(B)-P(A/C), in which each blockcopolymer is composed of a middle polymer block P(B) and two endcopolymer blocks P(A/C), where

[0031] P(B) represents a polymer of the monomers B which possesses asoftening/glass transition temperature of from 0° C. to −80° C., itbeing possible for component B to comprise one or more monomers, andwhere the softening/glass transition temperature of the block P(B) isbelow 0° C.,

[0032] P(A/C) represents a polymer of at least two monomers A and C, theblock P(A/C) possessing a softening/glass transition temperature of from20° C. to 175° C. and component C being selected from the group ofmonomers which as homopolymers have a softening/glass transitiontemperature of more than 60° C. or are capable of UV crosslinking,

[0033] The polymer block P(B) is insoluble in the copolymer blockP(A/C), and the blocks P(B) and P(A/C) are immiscible.

[0034] In an advantageous procedure use is made as component C, at leastquantitatively, of a compound which raises the softening/glasstransition temperature of the copolymer block P(A/C) to T_(G)>20° C. Ascomponents A and C it is preferred to select monomers which result inthe block P(A/C) being capable of forming a 2-phase domain structurewith the copolymer block P(B), in which case A and C may also beidentical.

[0035] The fraction of the polymer blocks P(A/C) is advantageouslybetween 20 and 70% by weight, in particular between 30 and 65% by weightof the overall block copolymer. With further advantage the weightfraction of component C in relation to component A is between 0 and 30%by weight, in particular between 0.5 and 15% by weight.

[0036] With advantage the structure of at least one block copolymer maybe described by one or more of the following general formulae:

P(A)-P(B)-P(A)   (I)

P(A)-P(B)-P(A)-P(B)-P(A)   (II)

[P(A)-P(B)]_(n)X   (III)

[P(A)-P(B)]_(n)X[P(B)]_(m)   (IV),

[0037] where n=3 to 12, m=3 to 12 and X represents a polyfunctionalbranching region,

[0038] where the polymer blocks P(A) independently of one anotherrepresent homopolymer or copolymer blocks of the monomers A, with thepolymer blocks P(A) each having a softening temperature in the rangefrom +20° C. to +175° C. and bearing at least one polar unit, such as acarboxylic acid, hydroxyl, amide, sulphonic acid or phosphoric acidgroup, for example,

[0039] and where the polymer blocks P(B) independently of one anotherrepresent homopolymer or copolymer blocks of the monomers B, with thepolymer blocks P(B) each having a softening temperature in the rangefrom −80° C. to 0° C.

[0040] With further advantage at least one block copolymer has asymmetrical structure such that polymer blocks P(A) identical in chainlength and/or chemical structure and/or polymer blocks P(B) identical inchain length and/or in chemical structure are present.

[0041] It is advantageous if at least one block copolymer meets one ormore of the following criteria:

[0042] a molecular weight of M_(n) of between 25 000 and 600 000 g/mol,preferably between 30 000 and 400 000 g/mol, more preferably between 50000 and 300 000 g/mol,

[0043] a polydispersity D=M_(w)/M_(n) of not more than 3,

[0044] a polymer blocks P(A) fraction between 15 and 70% by weight,preferably between 20 and 60% by weight, in particular between 30 and55% by weight, based on the triblock copolymer composition,

[0045] one or more grafted-on side chains.

[0046] The ratio of the chain lengths of the polymer blocks P(B) tothose of the polymer blocks P(A) can in particular be chosen such thatthe polymer blocks P(A) are present in the form of a disperse phase(“domains”) in a continuous matrix of the polymer blocks P(B).

[0047] It is additionally possible with advantage to use blends ofpolyacrylate-based block copolymers as repulpable PSAs. Thus it ispossible with outstanding effect to use a polymer blend of two or moreblock copolymers conforming to the above remarks, and also a blend ofone or more block copolymers conforming to the above remarks of at leastone diblock copolymer P(A)-P(B),

[0048] where the polymer blocks P(A) independently of one anotherrepresent homopolymer or copolymer blocks of the monomers A, with thepolymer blocks P(A) each having a softening/glass transition temperaturein the range from +20° C. to +175° C. and bearing at least one polarunit, such as a carboxylic acid, hydroxyl, amide, sulphonic acid orphosphoric acid group, for example,

[0049] and where the polymer blocks P(B) independently of one anotherrepresent homopolymer or copolymer blocks of the monomers B, with thepolymer blocks P(B) each having a softening/glass transition temperaturein the range from −80° C. to +10° C.

[0050] Also outstandingly possible for use in accordance with theconcept of the invention is a blend of at least two components K1 andK2, each component being based on at least one block copolymer P1 or P2,respectively,

[0051] where the at least one block copolymer P1 of component K1comprises at least the unit P(A1)-P(B1)-P(A1) composed of at least onepolymer block P(B1) and at least two polymer blocks P(A1), where

[0052] P(A1) independently at each occurrence represents homopolymer orcopolymer blocks of monomers A1, with the polymer blocks P(A1) eachhaving a softening/glass transition temperature in the range from +20°C. to +175° C. and bearing at least one polar unit, such as a carboxylicacid, hydroxyl, amide, sulphonic acid or phosphoric acid group, forexample,

[0053] P(B1) represents a homopolymer or copolymer block of monomers B1,with the polymer block P(B1) having a softening/glass transitiontemperature in the range from −80° C. to 0° C.,

[0054] the polymer blocks P(B1) and P(A1) are not homogeneously misciblewith one another,

[0055] where the at least one block copolymer P2 of component K2comprises at least the unit P(B2)-P(A2)-P(B2) composed of at least twopolymer blocks P(B2) and at least one polymer block P(A2), where

[0056] P(A2) represents a homopolymer or copolymer block of monomers A2,with the polymer block P(A2) having a softening/glass transitiontemperature in the range from +20° C. to +175° C. and bearing at leastone polar unit, such as a carboxylic acid, hydroxyl, amide, sulphonicacid or phosphoric acid group, for example,

[0057] P(B2) independently at each occurrence represents homopolymer orcopolymer blocks of monomers B2, with the polymer blocks P(B2) eachhaving a softening/glass transition temperature in the range from −80°C. to 0° C.,

[0058] the polymer blocks P(B2) and P(A2) are not homogeneously misciblewith one another,

[0059] and where the blend forms an at least two-phase system.

[0060] The ratio V of the amount m_(K2) of component K2 used in theblend to the amount m_(K1) of component K1 used in the blend isadvantageously up to 250 parts by weight of K2 per 100 parts by weightof K1, i.e. V=m_(K2)/m_(K1)≦2.5.

[0061] Preferably the blocks P(B1) are compatible with the blocks P(B2)and/or their respectively corresponding polymers P′(B1) with P′(B2)and/or the blocks P(A1) are compatible with the blocks P(A2) and/ortheir respectively corresponding polymers P′(A1) with P′(A2).

[0062] With further advantage the polymer blocks P(B1) and the polymerblocks P(B2) and/or the polymer blocks P(A1) and the polymer blocksP(A2) possess an identical homopolymer and/or copolymer composition.

[0063] It is advantageous if the average chain length LA2 of the polymerblocks P(A2) of the block copolymer P2 does not exceed the average chainlength LA1 of the polymer block P(A1) of the block copolymer P1; moreadvantageously LA2 is at least 10% smaller than LA1, very advantageouslyLA2 is at least 20% smaller than LA1.

[0064] It is further of advantage if the polymer blocks P(Au) (i=1, 2, .. . ) are present in the form of a disperse phase (“domains”) in acontinuous matrix of the polymer blocks P(Bi), preferably in the form ofspherical or distortedly spherical domains, this state being obtained inparticular by adjusting the ratio V_(Li) of the average chain lengthsLAi of the polymer blocks P(Ai) to the average chain lengths LBi of thepolymer blocks P(Bi) of the block copolymers Pi, very preferably byadjusting the ratio V_(L1) of the block copolymer P1.

[0065] As well as the particularly suitable PSAs above, mention may alsobe made of those having star structures, corresponding for instance to

[P(A)-P(B)]_(n)X

[P(B)-P(A)]_(n)X

[P(B)-P(A)-P(B)]_(n)X

[P(A)-P(B)-P(A)]_(n)X

[0066] or, generally,

[0067] where m and n independently of one another are integers greaterthan or equal to 1 and at least m or n is greater than or equal to 1; pand q independently are an integer greater than or equal to 0, and Xrepresents a polyfunctional branching unit, i.e. a chemical structuralelement by way of which two or more polymer arms are linked to oneanother. It is also possible here for two or more branching units to bepresent in the polymers. X is generally determined by the polymerizationprocess and can be aliphatic or else aromatic in nature. X may alsocontain heteroatoms, such as sulphur, for example. Generally speaking,star-shaped polymers can be prepared by means of polyfunctionalinitiators, or controlled or living block copolymers are reacted with apolyfunctional reactive unit.

[0068] Monomers

[0069] The monomers A for the copolymer blocks P(A) and/or P(A/C) of thePSAs used in accordance with the invention are preferably selected suchthat the resulting blocks P(A) and/or P(A/C) are capable of forming a2-phase domain structure with the copolymer blocks P(B) and/or P(B/D). Aprerequisite for this is the immiscibility of the blocks P(B) or P(B/D)with the blocks P(A) or P(A/C), respectively. Within the 2-phase domainstructure, regions are formed in which the blocks of different chains(and where appropriate also of identical chains) of one and the samemonomer variety mix with one another. These domains, as they are called,are embedded in a matrix of the blocks of the other monomer variety. Acharacteristic possessed by such a 2-phase domain structure is that ofhaving two softening/glass transition temperatures. With the formationof two phases of different properties, hard volume elements are obtainedalongside soft volume elements.

[0070] Advantageous examples of compounds used as component A includeacrylic acid, itaconic acid, methacrylic acid, hydroxyethyl acrylate,hydroxypropyl acrylate, hydroxyethyl methacrylate, hydroxypropylmethacrylate, acrylamide, vinylphosphonic acid, vinylsulphonic acid andsodium vinylsulphonate.

[0071] As component A it is also possible to use zwitterionic monomers,such as the group of the betaines, for example. Examples of suitablebetaines include ammonium carboxylates, ammonium phosphates and ammoniumsulphonates. Specific examples includeN-(3-sulphopropyl)-N-acryloyloxyethyl-N,N-dimethylammonium betaine,1-(3-sulphopropyl)-2-vinylpyridinium betaine andN-(3-sulphopropyl)-N-allyl-N,N-dimethyl-ammonium betaine. Especiallypreferred examples areN-(3-sulphopropyl)-N-methacryloyloxyethyl-N,N-dimethylammonium betaineand N-(3-sulphopropyl)-N-acryloyloxyethyl-N,N-dimethylammonium betaine.N-(3-Sulphopropyl)-N-meth-acryloyloxyethyl-N,N-dimethylammonium betaineis available commercially from Raschig AG, Germany. This enumerationmakes no claim to completeness.

[0072] As monomers B for the copolymer blocks P(B) and/or P(B/D) of thePSAs used in accordance with the invention it is advantageous to useacrylic monomers or vinyl monomers, more preferably those which lowerthe softening/glass transition temperature of the copolymer blockP(B/D)—alone or in combination with monomer D—to below 0° C. Veryadvantageously for the PSA of the invention use is made as component Bof one or more compounds which can be described by the following generalformula:

[0073] In this formula R₁=H or CH₃ and the radical R₂ is selected fromthe group of branched and unbranched, saturated alkyl groups having 4 to14 carbon atoms.

[0074] Acrylic monomers which are used with preference for the inventivePSA as component B include acrylic and methacrylic esters with alkylgroups composed of 4 to 18 carbon atoms, preferably 4 to 9 carbon atoms.Specific examples, without wishing to be restricted by this enumeration,include n-butyl acrylate, n-pentyl acrylate, n-hexyl acrylate, n-heptylacrylate, n-octyl acrylate, n-nonyl acrylate and their branched isomers,such as 2-ethylhexyl acrylate, for example.

[0075] Used additionally, optionally, as monomer B are vinyl monomersfrom the following groups: vinyl esters, vinyl ethers, vinyl halides,vinylidene halides and vinyl compounds having aromatic rings andheterocycles in a position. Here again, mention may be madenon-exclusively of certain examples: vinyl acetate, vinyl formamide,ethyl vinyl ether, vinyl chloride, vinylidene chloride andacrylonitrile.

[0076] As monomers C it is preferred to use acrylic monomers or vinylmonomers which raise the softening/glass transition temperature of thecopolymer block P(A/C)—alone or in combination with monomer A—to above20° C. In one advantageous version of the process of the invention(meth)acrylic monomers are used, especially those corresponding to thefollowing general formula:

[0077] where R₃=H or CH₃ and the radical —OR₄ constitutes or comprisesthe functional group for increasing the cohesion of the PSA.

[0078] Examples of component C include methyl methacrylate, cyclohexylmethacrylate, t-butyl acrylate, allyl alcohol, isobornyl methacrylate,isobornyl acrylate, maleic anhydride, itaconic anhydride, benzoinacrylate, acrylated benzophenone, acrylamides (such asN-t-butylacrylamide, N-isopropylacrylamide and dimethylacrylamide, forexample) and. glyceridyl methacrylate, benzyl acrylate, benzylmethacrylate, phenyl acrylate, phenyl methacrylate, t-butylphenylacrylate, t-butylphenyl methacrylate, 4-biphenylyl acrylate, 2-naphthylacrylate and 2-naphthyl methacrylate, this enumeration not beingconclusive.

[0079] Preferred choices here are as follows:

[0080] a) for dipole-dipole interaction and/or hydrogen bond formationproperties: acrylamides, methyl methacrylate

[0081] b) for crosslinking with high-energy radiation: benzoin acrylate,acrylated benzophenone

[0082] c) for thermal crosslinking: maleic anhydride, itaconicanhydride, glyceridyl methacrylate, but also all acrylamides.

[0083] With t-butyl acrylate an additional increase is produced in thesoftening/glass transition temperature without an increase in polarity.

[0084] As monomers C use is further made of vinylaromatics, which mayalso be alkylated, functionalized or contain heteroatoms, and whichpossess C₄ to C₁₈ aromatic nuclei. Especially preferred examples includestyrene, α-methylstyrene, 4-vinylbenzoic acid, sodium4-vinylbenzenesulphonate, 4-vinylbenzyl alcohol, 2-vinyinaphthalene,4-vinylphenylboronic acid, 4-vinylpyridine, phenyl vinylsulfonate,3,4-dimethoxystyrene, vinylbenzotrifluoride, p-methoxystyrene,4-vinylanisole, 9-vinylanthracene, 1-vinylimidazole, 4-ethoxystyrene andN-vinylphthalimide, this enumeration making no claim to completeness.

[0085] Component C may additionally be a UV photoinitiator which isequipped with a copolymerizable vinyl group and which is capable ofradiation-chemical crosslinking, in particular of a crosslinking inducedby UV irradiation.

[0086] Suitable photoinitiators are Norrish I and II photoinitiators.Examples include benzoin acrylate and an acrylated benzophenone from UCB(Ebecryl P 36®). This enumeration is not complete. In principle it ispossible to copolymerize any photoinitiators which are known to theperson skilled in the art and are able to crosslink the polymer by wayof a free-radical mechanism under UV radiation. An overview of possiblephotoinitiators which can be used, and which may be functionalized witha double bond, is given in Fouassier: “Photoinitiation,Photopolymerization and Photocuring: Fundamentals and Applications”,Hanser-Verlag, Munich 1995. Further details can be found in Carroy etal. in “Chemistry and Technology of UV and EB Formulation for Coatings,Inks and Paints”, Oldring (ed.), 1994, SITA, London.

[0087] As component D use is made in one preferred version of monomerswhich bear a functional group. The functional group of component D is agroup capable of crosslinking reaction through the effect, for example,of thermal energy. With advantage the functional group of component D ischosen to be a hydroxyl, carboxyl, epoxy, acid amid, isocyanato or aminogroup. Specific examples of monomer D therefore include acrylic acid,hydroxyethyl acrylate, hydroxypropyl acrylate, methacrylic acid, methylmethacrylate, hydroxyethyl methacrylate, hydroxypropyl methacrylate,tert-butyl acrylate, itaconic anhydride, itaconic acid, acrylamides,such as N-tert-butylacrylamide, N-isopropylacrylamide ordimethylacrylamide, for example, and maleic anhydride.

[0088] With advantage the functional group of component D that iscapable of crosslinking can be an unsaturated group which is capable ofradiation-chemical crosslinking, in particular a crosslinking which isinduced by means of UV radiation or by irradiation with electron beams.It has been found to be advantageous if the crosslinking-capablefunctional group of component D is an unsaturated alkyl radical having 3to 8 carbon atoms which contains at least one C—C double bond.

[0089] As monomers for component D it is possible with advantage to useat least one compound of the following general formula

[0090] where R₁=H or CH₃ and —OR₂ constitutes or comprises thefunctional group as above. In this case component D can be chosen suchthat it lowers the softening/glass transition temperature of thecopolymer block P(B/D) to T_(G)≦0° C.

[0091] Component D may alternatively be a UV photoinitiator which isequipped with a copolymerizable vinyl group and which is capable ofradiation-chemical crosslinking, in particular of a crosslinking inducedby UV irradiation.

[0092] Suitable photoinitiators are Norrish I and II photoinitiators.Examples include benzoin acrylate and an acrylated benzophenone from UCB(Ebecryl P 36®). This enumeration is not complete. In principle it ispossible to copolymerize any photoinitiators which are known to theperson skilled in the art and are able to crosslink the polymer by wayof a free-radical mechanism under UV radiation. An overview of possiblephotoinitiators which can be used, and which maybe functionalized with adouble bond, is given in Fouassier: “Photoinitiation,Photopolymerization and Photocuring: Fundamentals and Applications”,Hanser-Verlag, Munich 1995. Further details can be found in Carroy etal. in “Chemistry and Technology of UV and EB Formulation for Coatings,Inks and Paints”, Oldring (ed.), 1994, SITA, London.

[0093] Polymerizations

[0094] The polymerization can be conducted in accordance with or inmodification of a process known per se, in particular by conventionalradical polymerization and/or by controlled radical polymerization; thelatter is characterized by the presence of suitable control reagents.

[0095] For preparing the block copolymers it is possible in principle touse any polymerizations which proceed in accordance with a controlled orliving mechanism, and also combinations of different controlledpolymerization processes. Here mention may be made, for example, withoutmaking any claim to completeness, and in addition to anionicpolymerization, of ATRP, nitroxide/TEMPO-controlled polymerization or,more preferably, of the RAFT process; i.e. in particular processes whichallow control of the block lengths, of the polymer architecture or else,but not necessarily, of the tacticity of the polymer chain.

[0096] Radical polymerizations can be conducted in the presence of anorganic solvent or in the presence of water or in mixtures of organicsolvents and/or organic solvents with water, or without aqueous or othersolvent. It is preferred to use as little solvent as possible. Thepolymerization time for radical processes, depending on conversion andtemperature, is typically between 4 and 72 h.

[0097] In the case of solution polymerization the solvents used arepreferably esters of saturated carboxylic acids (such as ethyl acetate),aliphatic hydrocarbons (such as n-hexane, n-heptane or cyclohexane),ketones (such as acetone or methyl ethyl ketone), special boiling pointspirit, aromatic solvents such as toluene or xylene, or mixtures ofaforementioned solvents. For polymerization in aqueous media or inmixtures of organic and aqueous solvents it is preferred to addemulsifiers and/or stabilizers to the polymerization.

[0098] Where a radical polymerization method is employed thepolymerization initiators used advantageously include customaryradical-forming compounds such as peroxides, azo compounds and peroxosulphates, for example. Initiator mixtures also possess outstandingsuitability.

[0099] In an advantageous procedure radical stabilization is effectedusing nitroxides of type (VIIa) or (VIIb):

[0100] where R³, R⁴, R⁵, R⁶, R⁷, R⁸, R⁹ and R¹⁰ independently of oneanother denote the following compounds or atoms:

[0101] i) halides, such as chlorine, bromine or iodine,

[0102] ii) linear, branched, cyclic and heterocyclic hydrocarbons having1 to 20 carbon atoms, which can be saturated, unsaturated or aromatic,

[0103] iii) esters —COOR″, alkoxides —OR¹² and/or phosphonates—PO(OR¹³)₂, in which R″, R¹² and R¹³ stand for radicals from group ii).

[0104] Compounds of formula (VIIa) or (VIIb) can also be attached topolymer chains of any kind (primarily in the sense that at least one ofthe abovementioned radicals constitutes such a polymer chain) and cantherefore be used as macroradicals or macroregulators to construct theblock copolymers.

[0105] More preferred as controlled regulators for the polymerizationare compounds of the following type:

[0106] 2,2,5,5-tetramethyl-1-pyrrolidinyloxyl (PROXYL),3-carbamoyl-PROXYL, 2,2-dimethyl-4,5-cyclohexyl-PROXYL, 3-oxo-PROXYL,3-hydroxylimine-PROXYL, 3-aminomethyl-PROXYL, 3-methoxy-PROXYL,3-t-butyl-PROXYL, 3,4-di-t-butyl-PROXYL;

[0107] 2,2,6,6-tetramethyl-1-piperidinyloxyl (TEMPO),4-benzoyloxy-TEMPO, 4-methoxy-TEMPO, 4-chloro-TEMPO, 4-hydroxy-TEMPO,4-oxo-TEMPO, 4-amino-TEMPO, 2,2,6,6-tetraethyl-1-piperid inyloxyl,2,2,6-trimethyl-6-ethyl-1 -piperid inyloxyl;

[0108] N-tert-butyl 1-phenyl-2-methylpropyl nitroxide;

[0109] N-tert-butyl 1-(2-naphthyl)-2-methylpropyl nitroxide;

[0110] N-tert-butyl 1-diethylphosphono-2,2-dimethylpropyl nitroxide;

[0111] N-tert-butyl 1-dibenzylphosphono-2,2-dimethylpropyl nitroxide;

[0112] N-(1-phenyl-2-methylpropyl) 1-diethylphosphono-1-methylethylnitroxide;

[0113] di-t-butyl nitroxide;

[0114] diphenyl nitroxide;

[0115] t-butyl t-amyl nitroxide.

[0116] U.S. Pat. No. 4,581,429 A discloses a controlled-growth radicalpolymerization process initiated using a compound of the formulaR′R″N—O—Y in which Y is a free radical species which is able topolymerize unsaturated monomers. The reactions, however, generally havelow conversions. A particular problem is the polymerization ofacrylates, which proceeds only to very low yields and molar masses. WO98/13392 A1 describes open-chain alkoxyamine compounds which have asymmetrical substitution pattern. EP 735 052 A1 discloses a process forpreparing thermoplastic elastomers having narrow molar massdistributions. WO 96/24620 A1 describes a polymerization process usingvery specific radical compounds such as, for example,phosphorus-containing nitroxides which are based on imidazolidine. WO98/44008 A1 discloses specific nitroxyls based on morpholines,piperazinones and piperazinediones. DE 199 49 352 A1 describesheterocyclic alkoxyamines as regulators in controlled-growth radicalpolymerizations. Corresponding further developments of the alkoxyaminesor of the corresponding free nitroxides enhance the efficiency forpreparing polyacrylates (Hawker, Contribution to the National Meeting ofthe American Chemical Society, Spring 1997; Husemann, Contribution tothe IUPAC World Polymer Meeting 1998, Gold Coast).

[0117] As a further controlled polymerization method it is possibleadvantageously to use atom transfer radical polymerization (ATRP) tosynthesize block copolymers, with preferably monofunctional ordifunctional secondary or tertiary halides being used as initiators and,to abstract the halide(s), complexes of Cu, Ni, Fe, Pd, Pt, Ru, Os, Rh,Co, Ir, Ag or Au (EP 0 824 111 A1; EP 826 698 A1; EP 824 110 A1; EP 841346 A1; EP 850 957 A1). The different possibilities of ATRP are furtherdescribed in U.S. Pat. No. 5,945,491 A, U.S. Pat. No. 5,854,364 A andU.S. Pat. No. 5,789,487 A.

[0118] It is also possible with advantage to prepare the block copolymerused in accordance with the invention by way of an anionicpolymerization. In this case the reaction medium used preferablycomprises inert solvents, such as aliphatic and cycloaliphatichydrocarbons, for example, or else aromatic hydrocarbons.

[0119] The living polymer is generally represented by the structureP_(L)(A)-Me, where Me is a metal from group 1, such as lithium, sodiumor potassium and P_(L)(A) is a growing polymer block of the monomers A.The molar mass of the polymer block under preparation is determined bythe ratio of initiator concentration to monomer concentration. In orderto construct the block structure, first of all the monomers A are addedfor the construction of a polymer block P(A), then, by adding themonomers B, a polymer block P(B) is attached and subsequently, by againadding monomers A, a further polymer block P(A) is polymerized on, so asto form a triblock copolymer P(A)-P(B)-P(A). Alternatively, P(A)-P(B)-Mcan be coupled by means of a suitable difunctional compound. In this wayit is also possible to obtain starblock copolymers (P(B)-P(A))_(n).Examples of suitable polymerization initiators include n-propyllithium,n-butyllithium, sec-butyllithium, 2-naphthyllithium, cyclohexyllithiumand octyllithium, but this enumeration makes no claim to completeness.Initiators based on samarium complexes are also known for thepolymerization of acrylates (Macromolecules, 1995, 28, 7886) and can beused here.

[0120] It is also possible, moreover, to use difunctional initiators,such as 1,1,4,4-tetraphenyl-1,4-dilithiobutane or1,1,4,4-tetraphenyl-1,4-dilithioisobutane, for example. Coinitiators maylikewise be employed. Suitable coinitiators include lithium halides,alkali metal alkoxides or alkylaluminium compounds. In one verypreferred version the ligands and coinitiators are chosen so thatacrylate monomers, such as n-butyl acrylate and 2-ethylhexyl acrylate,for example, can be polymerized directly and do not have to be generatedin the polymer by transesterification with the corresponding alcohol.

[0121] After the anionic polymerization it is advisable, in order toliberate the polar groups, to carry out a polymer-analogous reaction.One possibility of preparing acrylate block copolymers functionalizedwith carboxylic acid groups involves the anionic polymerization oftert-butyl acrylate, after which the tert-butyl group can be hydrolysedwith trifluoroacetic acid, thereby liberating the carboxylic acid group.

[0122] A very preferred preparation process conducted is a variant ofthe RAFT polymerization (reversible addition-fragmentation chaintransfer polymerization). The polymerization process is described indetail, for example, in WO 98/01478 A1 and WO 99/31144 A1. Suitable withparticular advantage for the preparation of triblock copolymers aretrithiocarbonates of the general structure R″′—S—C(S)—S—R″′(Macromolecules 2000, 33, 243-245), by means of which, in a first step,monomers for the end blocks P(A) are polymerized. Then, in a secondstep, the middle block P(B) is synthesized. Following the polymerizationof the end blocks P(A), the reaction can be terminated and reinitiated.It is also possible to carry out polymerization sequentially withoutinterrupting the reaction. In one very advantageous version, forexample, the trithiocarbonates (VIII) and (IX) or the thio compounds (X)and (XI) are used for the polymerization, in which φ can be a phenylring, which can be unfunctionalized or functionalized by alkyl or arylsubstituents attached directly or via ester or ether bridges, or can bea cyano group, or can be a saturated or unsaturated aliphatic radical.The phenyl ring φ may optionally bear one or more polymer blocks, inaccordance with the definition for P(A), P(B), P(A/C) and P(B/D).Examples of possible functionalizations include halogens, hydroxylgroups, epoxide groups, and groups containing nitrogen or sulphur,without this list making any claim to completeness.

[0123] It is also possible to employ thioesters of the general structureR^(IV)—C(S)—S—R^(V), particularly in order to prepare asymmetricsystems. R^(IV) and R^(V) may be chosen independently of one another:R^(IV) can be a radical from one of the following groups i) to iv) andR^(V) can be a radical from one of the following groups i) to iii):

[0124] In connection with the abovementioned polymerizations whichproceed by controlled radical mechanisms it is preferred to useinitiator systems which further comprise additional radical initiatorsfor the polymerization, especially thermally decomposing radical-formingazo or peroxo initiators. In principle, however, all customaryinitiators known for acrylates are suitable for this purpose. Theproduction of C-centred radicals is described in Houben-Weyl, Methodender Organischen Chemie, Vol. E19a, p.60 ff. These methods are employedpreferentially. Examples of radical sources are peroxides,hydroperoxides and azo compounds. A few non-exclusive examples oftypical radical initiators that may be mentioned here include thefollowing: potassium peroxodisulphate, dibenzoyl peroxide, cumenehydroperoxide, cyclohexanone peroxide, cyclohexyl-sulphonyl acetylperoxide, di-tert-butyl peroxide, azodiisobutyronitrile, diisopropylpercarbonate, tert-butyl peroctoate and benzpinacol. In one verypreferred version the radical initiator used is1,1′-azobis(cyclohexylnitrile) (Vazo 88®, DuPont®) or2,2-azobis-(2-methylbutanenitrile) (Vazo 67®, DuPont®). Furthermore, itis also possible to use radical sources which release radicals onlyunder UV irradiation.

[0125] In the conventional RAFT process, polymerization is generallycarried out only to low conversions (WO 98/01478 A1), in order to obtainvery narrow molecular weight distributions. Because of the lowconversions, however, these polymers cannot be used as PSAs andparticularly not as hotmelt PSAs, since the high residual monomerfraction adversely affects the adhesive performance properties, theresidual monomers contaminate the solvent recyclate in the concentrationprocess, and the corresponding self-adhesive tapes would exhibit veryhigh outgassing.

[0126] In accordance with the invention the solvent is stripped off,preferably in a concentrating extruder, under reduced pressure; for thispurpose it is possible to use, for example, single-screw or twin-screwextruders, which preferentially distil off the solvent in different orthe same vacuum stages and which possess a feed preheater.

[0127] For further development in accordance with the invention, it ispossible to admix tackifier resins to the block copolymer repulpablePSAs. In principle it is possible to use all resins which are soluble inthe corresponding polyacrylate blocks P(A), P(B), P(A/C) and P(B/D).Suitable tackifier resins include rosin and rosin derivatives (rosinesters, including rosin derivatives stabilized by, for example,disproportionation or hydrogenation), polyterpene resins,terpene-phenolic resins, alkylphenol resins, and aliphatic, aromatic andaliphatic-aromatic hydrocarbon resins, to name but a few. U.S. Pat. No.09/040,024, U.S. Pat. No. 6,133,391, U.S. Pat. No. 5,489,642 and U.S.Pat. No. 4,413,082 cite or specify further resins and plasticizerssuitable in particular for repulpable PSAs.

[0128] Primarily, the resins chosen are those which are preferablycompatible with the elastomer block. The weight fraction of the resinsin the block copolymer is typically up to 60% by weight, more preferablyup to 50% by weight.

[0129] For one specific way of carrying out the invention it is alsopossible to use resins which are specifically compatible in only one ofthe polymer blocks P(A), P(B), P(A/C), P(B/D). It is also possible,optionally, to add plasticizers, fillers (e.g. fibres (e.g. cellulosefibres, polyvinyl alcohol fibres), carbon black, zinc oxide, titaniumdioxide, chalk, solid or hollow glass beads, microbeads made of othermaterials, silica, silicates), nucleators, expandants, compoundingagents and/or ageing inhibitors, in the form for example of primary andsecondary antioxidants or in the form of light stabilizers.

[0130] The internal strength (cohesion) of the PSA is preferablyproduced by the physical phase separation of the polymer blocks. Theresultant physical crosslinking is typically thermoreversible. Forirreversible crosslinking the PSAs may additionally be crosslinkedchemically. For this purpose, the acrylic block copolymer PSAs which areused for the repulpable systems of the invention may optionally haveadded to them, in addition to components C and D, compatible crosslinkersubstances. Examples of suitable crosslinkers include metal chelates,polyfunctional isocyanates, polyfunctional amines or polyfunctionalalcohols. Polyfunctional acrylates as well can be used with advantage ascrosslinkers for actinic irradiation.

[0131] It may further be of advantage that the acidic groups of thecarboxylic acid, of the alcohols, of the sulphonic acid or of thephosphoric acids are deprotonated with bases, resulting in agglomerationwithin the phases. In the simplest case, basic organic and inorganiccompounds are used, such as NaOH, KOH, triethylamine, trimethylamine anddimethylamine, for example. It is, however, also possible to usepolyfunctional bases, such as polyfunctional amines, for example.

[0132] For optional crosslinking with UV light, UV-absorbingphotoinitiators are added to the polyacrylate block copolymers employedin the systems of the invention. Useful photoinitiators which can beused to great effect include benzoin ethers, such as benzoin methylether and benzoin isopropyl ether, substituted acetophenones, such as2,2-diethoxyacetophenone (available as Irgacure 651® from Ciba Geigy®),2,2-dimethoxy-2-phenyl-1-phenylethanone, dimethoxyhydroxyacetophenone,substituted a-ketols, such as 2-methoxy-2-hydroxypropiophenone, aromaticsulphonyl chlorides, such as 2-naphthylsulphonyl chloride, andphotoactive oximes, such as 1-phenyl-1,2-propane-dione2-(O-ethoxycarbonyl) oxime, for example.

[0133] The abovementioned photoinitiators and others which can be used,including those of the Norrish I or Norrish II type, may contain thefollowing radicals: benzophenone, aceto-phenone, benzil, benzoin,hydroxyalkylphenone, phenyl cyclohexyl ketone, anthraquinone,trimethylbenzoylphosphine oxide, methylthiophenyl morpholinyl ketone,aminoketone, azobenzoin, thioxanthone, hexaarylbisimidazole, triazine orfluorenone, it being possible for each of these radicals additionally tobe substituted by one or more halogen atoms and/or one or more alkyloxygroups and/or one or more amino groups or hydroxyl groups. Arepresentative overview is given by Fouassier: “Photoinitiation,Photopolymerization and Photocuring: Fundamentals and Applications”,Hanser-Verlag, Munich 1995. For further details, Carroy et al. in“Chemistry and Technology of UV and EB Formulation for Coatings, Inksand Paints”, Oldring (ed.), 1994, SITA, London, can be consulted.

[0134] In principle it is also possible to irradiate the repulpable PSAsused in accordance with the invention with electron beams. Typicalirradiation devices which may be employed include linear cathodesystems, scanner systems and segmented cathode systems, in the case ofelectron beam accelerators. A detailed description of the state of theart, and the most important process parameters, can be found inSkelhorne, Electron Beam Processing, in Chemistry and Technology of UVand EB Formulation for Coatings, Inks and Paints, Vol. 1, 1991, SITA,London. The typical acceleration voltages are situated within the rangebetween 50 kV and 500 kV, preferably between 80 kV and 300 kV. Thescatter doses employed range between 5 and 150 kGy, in particularbetween 20 and 100 kGy.

[0135] Product Constructions of the PSA Sheet Materials

[0136] The PSA tape can be produced by coating the PSA compositiondescribed above onto one or more surfaces of a backing. Single-sided anddouble-sided PSA tapes are obtainable by this means. Where a repulpablePSA tape is reproduced, the backing ought likewise to be repulpable.

[0137] For use as a PSA tape it may likewise be necessary to line thePSA with a release liner. Commercially available examples includesiliconized release papers.

[0138] It is also possible to apply the repulpable PSAs directly,without backing material. In this case, for example, the PSA is appliedby spraying.

[0139] As well as special repulpable paper backings it may also beadvantageous to apply the inventive PSAs to a conventional paperbacking. Suitable examples include graphics papers or papers for offsetprinting.

[0140] Besides the application of the repulpable PSAs or PSA tapes forthe papermaking process, the inventive PSAs can also be used forproducing labels, PSA masking tapes, self-adhesive postage stamps, andalso self-adhesive wall coverings or wall decorations.

EXAMPLES Test Methods

[0141] A. Repulpability

[0142] The test was conducted in analogy to the Tappi test method UM 213A for recyclable and water-dispersible pressure-sensitive adhesives. Thetest paper for the adhesive bond is “James River Pulp Testing Paperwhite 417-01-50” from Curtis Paper Division. The water hardness is 300mg CaO/l water, corresponding to 30 dH [German hardness].

[0143] B. Static Shear Test

[0144] First of all the PSA is applied from solution to a siliconizedrelease paper and then dried at 100° C. for 20 minutes. The coatweightis approximately 50 g/m². Then 13×20 mm strips are cut out and laminatedonto two graphics paper strips (Turbo-Press T54G Feldmühle AG) with awidth of 20 mm and a length of 100 mm. The long side of the rectangularPSA area were arranged along the paper strips at a distance of 3.5 mmfrom the corners. The splices were produced by exerting a pressure bymeans of a steel roller whose intrinsic weight was 2 kg. The steelroller was rolled 5 times over the splices at a speed of 0.2 m/s, afterwhich the splice was conditioned for 48 h at 23° C. and 55% atmospherichumidity. Thereafter a shearing force was exerted on the splice in thelongitudinal direction to the paper strips. With a shear weight of 10 N,the time taken for the PSA to shear off completely was measured, or theshear travel within a specific time is measured.

[0145] C. Gel Permeation Chromatography (GPC)

[0146] The average molecular weight M_(W) and the polydispersity PD weredetermined by gel permeation chromatography. The eluent used was THFcontaining 0.1% by volume of trifluoroacetic acid. Measurement was madeat 25° C. The precolumn used was PSS-SDV, 5μ, 10³ Å, ID 8.0 mm×50 mm.Separation was carried out using the columns PSS-SDV, 5μ, 10³ and also10⁵ and 10⁶, each with ID 8.0 mm×300 mm. The sample concentration was 4g/l and the flow rate 1.0 ml per minute. Measurement was made againstpolystyrene standards.

Production of Test Specimens

[0147] Preparation of a RAFT Regulator:

[0148] The regulator bis-2,2′-phenylethyl trithiocarbonate (formulaVIII) was prepared starting from 2-phenylethyl bromide using carbondisulphide and sodium hydroxide in accordance with a specification fromSynth. Comm., 1988, 18 (13), 1531. Yield 72%.

[0149]¹H-NMR (CDCl₃), δ: 7.20-7.40 ppm (m, 10 H); 3.81 ppm (m, 1 H);3.71 ppm (m, 1 H); 1.59 ppm (d, 3 H); 1.53 ppm (d, 3 H).

Example 1

[0150] A 2 l reactor conventional for radical polymerization is chargedunder nitrogen with 40 g of acrylic acid, 40 g of 2-ethylhexyl acrylate,1.2 g of bis-2,2′-phenylethyl trithiocarbonate regulator and 80 g ofacetone. Heating is carried out to an internal temperature of 60° C. andthe initial charge is initiated with 0.2 g of Vazo 67® (DuPont) insolution in 5 g of acetone. After a reaction time of 1.5 hoursinitiation is repeated with 0.2 g of Vazo 67® (DuPont) in solution in 5g of acetone. After 5 and 7 hours of reaction the batch is diluted ineach case with 50 g of acetone.

[0151] After a reaction time of 24 hours a sample is taken. Gelpermeation chromatography (Test C) against polystyrene standardsindicated M_(N)=30 100 g/mol and M_(W)=35 300 g/mol.

[0152] The polymerization is continued in the same reactor after areaction time of 24 h. To the polymer are added 320 g of 2-ethylhexylacrylate, 80 g of acetone and 20 g of isopropanol. After a reaction timeof 24.75 hours initiation is repeated with 0.2 g of Vazo 67® (DuPont) insolution in 5 g of acetone. After 28.5 hours and 32 hours dilution iscarried out with in each case 50 g of acetone. After 48 hours initiationis repeated with 0.2 g of Vazo 67® (DuPont) in solution in 5 g ofacetone. After 55.5 hours 20 g of acetone are added and after 72 hoursthe reaction is terminated by cooling to room temperature.

[0153] Gel permeation chromatography (Test C) against polystyrenestandards indicated M_(N)=41 900 g/mol and M_(W)=77 400 g/mol.

Example 2

[0154] A 2 l reactor conventional for radical polymerization is chargedunder nitrogen with 80 g of acrylic acid, 160 g of DMF and 0.8 g ofbis-2,2′-phenylethyl trithiocarbonate regulator. Heating is carried outto an internal temperature of 60° C. and the batch is initiated with 0.2g of Vazo 67®) (DuPont) in solution in 5 g of DMF. After a reaction timeof 48 hours the reaction mixture is cooled to room temperature and theDMF solvent (dimethylformamide) is distilled off on a rotary evaporator.Gel permeation chromatography (Test C) against polystyrene standardsindicated M_(N)=7 500 g/mol and M_(W)=15 200 g/mol.

[0155] The polymerization is continued in the same reactor after 24 h.To the polyacrylic acid are added 80 g of 2-ethylhexyl acrylate, 160 gof acetone and 40 g of ethanol. At an internal temperature of 60° C.initiation is carried out with 0.1 g of Vazo 67® (DuPont), in solutionin 5 g of acetone. After 24 hours initiation is repeated with 0.1 g ofVazo 67® (DuPont), in solution in 5 g of acetone and after 32 h thebatch is diluted with 50 g of acetone. After 48 h the reaction isterminated by cooling to room temperature.

[0156] Gel permeation chromatography (Test C) against polystyrenestandards indicated M_(N)=54 700 g/mol and M_(W)=103 800 g/mol.

Example 3

[0157] A 2 L reactor conventional for radical polymerization is chargedunder nitrogen with 80 g of acrylic acid, 160 g of DMF and 0.8 g ofbis-2,2′-phenylethyl trithiocarbonate regulator. Heating is carried outto an internal temperature of 60° C. and the batch is initiated with 0.2g of Vazo 67® (DuPont) in solution in 5 g of DMF. After a reaction timeof 48 hours the reaction mixture is cooled to room temperature and theDMF solvent (dimethylformamide) is distilled off on a rotary evaporator.Gel permeation chromatography (Test C) against polystyrene standardsindicated M_(N)=7 500 g/mol and M_(W)=15 200 g/mol.

[0158] The polymerization is continued in the same reactor after 24 h.To the polyacrylic acid are added 60 g of 2-ethylhexyl acrylate, 20 g ofacrylic acid, 160 g of acetone and 30 g of ethanol. At an internaltemperature of 60° C. initiation is carried out with 0.1 g of Vazo 67®(DuPont), in solution in 5 g of acetone. After 24 hours initiation isrepeated with 0.1 g of Vazo 67® (DuPont), in solution in 5 g of acetoneand after 32 h the batch is diluted with 50 g of acetone. After 48 h thereaction is terminated by cooling to room temperature.

[0159] Gel permeation chromatography (Test C) against polystyrenestandards indicated M_(n)=59 200 g/mol and M_(W)=110 300 g/mol.

[0160] Production of the PSA Material

[0161] 50 g of Examples 1, 2 and 3 (based on the polymer fraction) wereblended with in each case 115 g of ethoxylated liquid primary coconutoil amine. This plasticizer is based on a primary amine in which all ofthe hydrogen atoms have been substituted by ethoxylated side chains. Theplasticizer contains approximately 15 ethoxy units per amino functionand is available under the trade name Ethomeen C 25 from Akzo Nobel. 0.1g of bisphenol A bisglycidyl ether is added to each blend and a clearsolution is produced by adding water and acetone.

[0162] Results

[0163] The GPC measurements demonstrate that the polyacrylic acidprepared in the first step can be used to prepare, by reinitiation,block copolymers containing acrylic acid. The construction of the middleblock in the second step further significantly raises the molecularweight—a clear indication of sequential polymerization.

[0164] The polymers prepared (Examples 1 to 3) were then blended in eachcase with a plasticizer and with a thermal crosslinker. Repulpabilitywas tested by Test A and the internal strength by Test B. All ofExamples 1 to 3 were flawlessly repulpable by Test A. The results of thestatic shear test are listed below:

[0165] Example 1: 200 min

[0166] Example 2: 800 min

[0167] Example 3: >5 000 min

We claim:
 1. Repulpable pressure-sensitive adhesive comprising at leastone polyacrylate-based block copolymer.
 2. Repulpable pressure-sensitiveadhesive according to claim 1, wherein the block copolymer comprises asequence of hard polymer blocks [P(A)] having a softening/glasstransition temperature of not less than 20° C. and having at least onepolar unit and of soft polymer blocks [P(B)] having a softening/glasstransition temperature of not more than O° C.
 3. Repulpablepressure-sensitive adhesive according to claim 1, wherein the blockcopolymer has a triblock structure P(A)-P(B)-P(A) and/or P(B)-P(A)-P(B)where P(A) is a hard polymer block having a softening/glass transitiontemperature of not less than 20° C. and at least one polar unit and P(B)is a soft polymer block having a softening/glass transition temperatureof not more than 0° C.
 4. Repulpable pressure-sensitive adhesiveaccording to claim 1, wherein the block copolymer comprises a sequenceof hard polymer blocks [P(A)] having a softening/glass transitiontemperature of not less than 20° C. and having at least one polar unitand of soft polymer blocks [P(B)] having a softening/glass transitiontemperature of not more than 0° C. and the block copolymer in thepolymer blocks P(A) and/or P(B) comprises at least one comonomer havingat least one functional group which is inert in a free-radicalpolymerization reaction and which is able to promote a crosslinkingreaction of the block copolymers and/or raises the softening/ glasstransition temperature.
 5. Repulpable pressure-sensitive adhesiveaccording to claim 1, wherein the block copolymer has a P(A)-P(B/D)-P(A)structure, where P(B/D) represents a copolymer block of the monomers Band D and possesses a softening/glass transition temperature of from−80° C. to 0° C., component D possessing at least one functional groupwhich is inert in a free-radical polymerization reaction and serves toincrease the cohesion of the block copolymer; P(A) represents a polymerblock of the monomers A and possesses a softening/glass transitiontemperature of from 20° C. to 175° C. and bears at least one polar unit;and the polymer block P(A) is insoluble in the copolymer block P(B/D)and the polymer block P(A) and the copolymer block P(B/D) areimmiscible.
 6. Repulpable pressure-sensitive adhesive according to claim5, wherein the fraction of the polymer blocks P(A) in the blockcopolymer is from 10 to 60% by weight.
 7. Repulpable pressure-sensitiveadhesive according to claim 5, wherein the fraction of component D inthe copolymer block P(B/D) is from 0.5 to 30% by weight.
 8. Repulpablepressure-sensitive adhesive according to claim 1, wherein the blockcopolymer has a P(B)-P(A)-P(B) or P(B/D)-P(A)-P(B/D) structure, whereP(B) represents a polymer block of the monomers B and possesses asoftening/glass transition temperature of not more than 0° C.; P(B/D)represents a copolymer block of the monomers B and D and possesses asoftening/glass transition temperature of not more than 0° C., componentD possessing at least one functional group which is inert in afree-radical polymerization reaction and which serves to increase thecohesion of the block copolymer; P(A) represents a polymer block of themonomers A and possesses a softening/glass transition temperature of notless than 20° C. and bears at least one polar unit; and the polymerblock P(A) is insoluble in the polymer block P(B) or in the copolymerblock P(B/D) and the polymer block P(B) and also the copolymer blockP(B/D) and P(A) are immiscible.
 9. Repulpable pressure-sensitiveadhesive according to claim 8, wherein the fraction of the polymerblocks P(A) in the block copolymer is from 30 to 70% by weight. 10.Repulpable pressure-sensitive adhesive according to claim 8, wherein thefraction of component D in the copolymer block P(B/D) is from 0.5 to 30%by weight.
 11. Repulpable pressure-sensitive adhesive according to claim1, wherein the block copolymer has a P(A/C)-P(B)-P(A/C) structure, whereP(B) represents a polymer block of the monomers B and possesses asoftening/glass transition temperature of from −80° C. to 0° C.; P(A/C)represents a polymer of at least two monomers A and C and possesses asoftening/glass transition temperature of from 20° C. to 175° C.,component C being selected from the group of monomers which ashomopolymers have a softening/glass transition temperature of greaterthan 60° C. or are capable of UV crosslinking; and the polymer blockP(B) is insoluble in the copolymer block P(A/C) and the polymer blockP(B) and the copolymer block P(A/C) are immiscible.
 12. Repulpablepressure-sensitive adhesive according to claim 11, wherein the fractionof the copolymer blocks P(A/C) in the block copolymer is from 30 to 65%by weight.
 13. Repulpable pressure-sensitive adhesive according to claim11, wherein the fraction of component C in the copolymer block P(A/C) isfrom 0.5 to 30% by weight.
 14. Repulpable pressure-sensitive adhesiveaccording to claim 1, wherein the block copolymer has a [P(A)-P(B)]_(n)Xstructure or a [P(A)-P(B)]_(n)X[P(B)]_(m) structure, where n is aninteger from 3 to 12, m is an integer from 3 to 12 and X represents apolyfunctional branching region; P(A) represents a polymer block of themonomers A and possesses a softening/glass transition temperature in therange from 20° C. to 175° C. and bears at least one polar unit; and P(B)represents a polymer block of the monomers B and has a softening/glasstransition temperature in the range from −80° C. to 0° C.
 15. Repulpablepressure-sensitive adhesive tape comprising a backing material, whereinat least one side of the backing material is provided with apressure-sensitive adhesive according to any one of the precedingclaims.
 16. A method of splicing papers, which comprises splicing saidpapers with a repulpable pressure-sensitive adhesive tape of claim 15.